Polarizer

ABSTRACT

There is provided a polarizer constituted by a polarizing element, and at least one transparent protective film constituted by two layers of retardation films with an in-plane retardation in a range of from 190 to 320 nm with respect to light having a wavelength of 550 nm. The transparent protective film is bonded onto one of opposite surfaces of the polarizing element so that a slow axis of each of the retardation films is parallel with an absorption axis of the polarizing element. The two layers of retardation films are constituted by a combination of a retardation film with Nz of from 0.8 to 0.95 and a retardation film with Nz of from 0.55 to 0.7 in the condition of nx&gt;ny and Nz=(nx−nz)/(nx−ny) in which nx and ny are in-plane refractive indices of the retardation films respectively, and nz is a refractive index in a direction of thickness of each of the retardation films.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a polarizer by which lightleakage based on changes of polarizing element axes caused by a changeof a viewing angle in between polarizing elements disposed in the formof crossed-Nicol can be prevented in a wide-range visible light regionto thereby achieve liquid-crystal display of a wide viewing angle, orthe like.

[0003] The present application is based on Japanese Patent ApplicationNo. 2000-330069, which is incorporated herein by reference.

[0004] 2. Description of the Related Art

[0005] In polarizing elements disposed in the form of crossed-Nicol,there was a problem that light leakage might occur when the azimuth waschanged to an oblique one even in the case where the light could be cutoff ordinarily in a normal-line (frontal) direction. This was becausethe relationship in crossed-Nicol optical axis is displaced or collapsedbetween the polarizing elements due to the change of the apparent anglecaused by the oblique view. As a background-art device to solve thelight leakage problem caused by such an azimuth angle, there was known apolarizer in which a transparent protective film exhibitingbirefringence with a retardation of from 190 to 320 nm and with Nz(which will be described later) of from 0.1 to 0.9 was disposed so thatthe slow axis of the transparent protective film is parallel with theabsorption axis of a polarizing element (see Unexamined Japanese PatentPublication No. Hei. 4-305602).

[0006] The background-art polarizer was provided to compensate for thedisplacement in absorption axis or the like between polarizing elementsdue to the change of the viewing angle as follows. As a transparentprotective film to be bonded to one or each of opposite surfaces of apolarizing element for improving durability against penetration ofmoisture or the like, a film exhibiting retardation characteristic ofabout a half wavelength with respect to visible light was used insteadof an isotropic transparent protective film constituted by atriacetylcellulose (TAC) film or the like exhibiting littlebirefringence. There was, however, a problem that the compensatingmeasure could not cope with wavelength dispersion.

[0007] That is, wavelength dispersion, which is a phenomenon that theretardation varies in accordance with the wavelength, generally occursin a retardation film. Hence, the function of the retardation film as ahalf-wave plate works only for light with a specific wavelength. Forlight with the other wavelengths, the retardation film cannot functionas a half-wave plate accurately, so that the light with the otherwavelengths is inferior in the characteristic of linearly polarizedlight. There therefore arises a coloring problem. Incidentally, when thecharacteristic of the retardation film is optimized to compensate forlight with a wavelength near to 550 nm exhibiting the maximum luminousefficacy, light with the other wavelengths is colored with blue becausethe condition for the light is displaced from the aforementionedoptimizing condition. Hence, when the retardation film is applied to aliquid-crystal display device or the like, the coloring problem revealsitself as a problem in deterioration of neutral characteristic ofdisplay.

SUMMARY OF THE INVENTION

[0008] An object of the present invention is to develop a polarizer inwhich light leakage hardly occurs while coloring owing to wavelengthdispersion hardly occurs to thereby achieve excellent neutralcharacteristic even in the case where polarizing elements disposed inthe form of crossed-Nicol are obliquely viewed at an azimuth displacedfrom the optical axis thereof.

[0009] According to the present invention, there is provided a polarizerconstituted by: a polarizing element; and at least one transparentprotective film constituted by two layers of retardation films with anin-plane retardation in a range of from 190 to 320 nm with respect tolight having a wavelength of 550 nm, the transparent protective filmbeing bonded onto one of opposite surfaces of the polarizing element sothat a slow axis of each of the retardation films is parallel with anabsorption axis of the polarizing element, the two layers of retardationfilms being constituted by a combination of a retardation film with Nzof from 0.8 to 0.95 and a retardation film with Nz of from 0.55 to 0.7in the condition of nx>ny and Nz=(nx −nz)/(nx−ny) in which nx and ny arein-plane refractive indices of the retardation films respectively, andnz is a refractive index in a direction of thickness of each of theretardation films.

[0010] According to the present invention, there can be obtained apolarizer which exhibits a compensating function for canceling thechange of an optical axis such as an absorption axis of a polarizingelement by changing an optical axis such as a slow axis of each ofretardation films constituting a transparent protective film inaccordance with the change of a viewing angle so that both light leakageand wavelength dispersion of retardation can be suppressed not only at aviewing angle parallel with the optical axis of polarizing elementsdisposed in the form of crossed-Nicol but also at a viewing angledisplaced from the optical axis to thereby achieve excellent neutralcharacteristic (colorlessness) and make linear polarizing characteristicunchangeable. The use of the polarizer permits the formation of aliquid-crystal display device, or the like, excellent in display qualitysuch as high contrast ratio at a wide viewing angle. In addition, thepolarizer is excellent in reduction of thickness and weight because thetwo layers of retardation films serve as a transparent protective film.

[0011] Features and advantages of the invention will be evident from thefollowing detailed description of the preferred embodiments described inconjunction with the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] In the accompanying drawings:

[0013]FIG. 1 is an explanatory view showing an embodiment of the presentinvention;

[0014]FIGS. 2A to 2C are model views each showing a state in which theaxis of the polarizer is displaced in accordance with the change of theviewing angle; and

[0015]FIG. 3 is an explanatory view showing the measurement ofspectroscopic intensity.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The polarizer according to the present invention is constitutedby: a polarizing element; and at least one transparent protective filmconstituted by two layers of retardation films with an in-planeretardation in a range of from 190 to 320 nm with respect to lighthaving a wavelength of 550 nm, the transparent protective film beingbonded onto one of opposite surfaces of the polarizing element so that aslow axis of each of the retardation films is parallel with anabsorption axis of the polarizing element, the two layers of retardationfilms being constituted by a combination of a retardation film with Nzof from 0.8 to 0.95 and a retardation film with Nz of from 0.55 to 0.7in the condition of nx>ny and Nz=(nx −nz)/(nx−ny) in which nx and ny arein-plane refractive indices of the retardation films respectively, andnz is a refractive index in a direction of thickness of each of theretardation films. FIG. 1 shows an example of the polarizer. In FIG. 1,the polarizer has a polarizing element 1, transparent protective films 2and 3, and an adhesive agent layer 4. The transparent protective film 2has two layers constituted by retardation films 21 and 22.

[0017] As the polarizing element, it is possible to use a suitable onecapable of transmitting linearly polarized light when natural light ismade incident on the polarizing element, without any particularlimitation. The preferred polarizing element is a polarizing element bywhich transmitted light excellent in the degree of polarization can beobtained with good light transmittance. From this point of view, it ispreferable to use an absorption-dichromatic polarizing element whichtransmits linearly polarized light while absorbing the other light whennatural light is made incident on the polarizing element. Particularlyfrom the point of view of handling properties such as reduction inthickness, flexibility, and so on, the absorption-dichromatic polarizingelement is preferably made of a polarizing film. Incidentally, theabsorption-dichromatic polarizing element may be constituted by anoriented layer obtained by applying a liquid-crystal dichromatic dye.

[0018] As the absorption-dichromatic polarizing element made of apolarizing film, it is also possible to use any suitable one. From thepoint of view of obtaining linearly polarized light in a wide-rangevisible light wavelength region, or the like, it is possible to use apolyvinyl alcohol film made of a polymer such as polyvinyl alcohol orpartially formalized polyvinyl alcohol, the film being drawn andoriented after impregnated with iodine or/and a dichromatic dye such asan azo dye, an anthraquinone dye, a tetrazine dye, or the like, by asuitable system such as an adsorption system. Especially, a uniaxiallydrawn film is preferably used.

[0019] As shown in FIG. 1, the transparent protective films 2 and 3 arebonded/laminated onto one or both of opposite surfaces of the polarizingelement 1. In the present invention, at least the transparent protectivefilm 2, which is disposed on one of the opposite surfaces of thepolarizing element 1, is made of two layers of retardation films 21 and22 constituted by a combination of a retardation film with Nz of from0.8 to 0.95 and a retardation film with Nz of from 0.55 to 0.7, each ofthe retardation films exhibiting an in-plane retardation of from 190 to320 nm with respect to light having a wavelength of 550 nm. In the abovedescription, Nz is defined by the expression: Nz=(nx−nz)/(nx−ny) in thecondition of nx>ny when nx and ny are in-plane refractive indices ofeach retardation film, and nz is a refractive index in a direction ofthe thickness of each retardation film.

[0020] In the above description, the two layers of retardation films arebonded/laminated to/on each other so that the slow axis of each of theretardation films is parallel with the absorption axis of the polarizingelement. The parallel relationship between the slow axis and theabsorption axis does not mean a perfect parallel state in terms ofproduction accuracy or the like. In terms of the compensating effect,however, the smaller the crossing angle between the two axes, the betterthe relationship between the two axes. In this case, the slow axis ofeach of the retardation films and the absorption axis of the polarizingelement are based on the viewing angle from the front (azimuth angle:0). The sequence of laminating the retardation films with different Nzcan be selected at option. In FIG. 1, the retardation film 22 with Nz offrom 0.55 to 0.7 is bonded/laminated onto the polarizing element 1through the retardation film 21 with Nz of from 0.8 to 0.95. Thissequence of arrangement is preferred from the point of view of thecompensating effect. Incidentally, the in-plane retardation can becalculated as a product (Δn·d) of the refractive index difference(Δn=nx−ny) and the thickness (d) of each of the retardation films.

[0021] For example, each of the retardation films can be obtained as abirefringent film constituted by a high molecular film drawn by asuitable system such as a uniaxial drawing system, a biaxial drawingsystem, or the like. A retardation film excellent in light transmittanceand little in orientation unevenness and retardation unevenness is usedpreferably. A retardation film exhibiting the aforementionedcharacteristics of retardation and Nz can be formed by a suitable methodsuch as a method in which a heat-shrinkable film is bonded to a highmolecular film and oriented under the function of shrinking force of theheat-shrinkable film by heating to there by control the refractive indexin the direction of the thickness thereof, a method in which a highmolecular film is obtained while controlling orientation by applying anelectric field in the direction of the thickness thereof and is drawn,or the like. In this case, the retardation and Nz can be changed bychanging the kind of polymer of the film as a subject of the process,the drawing condition, the kind of the heat-shrinkable film, the appliedvoltage, and so on. Incidentally, in a general drawing process such as auniaxial drawing process, Nz is set to be not larger than 0 or notsmaller than 1.

[0022] As the high molecular compound forming the retardation film, itis possible to use a suitable one without any particular limitation.Especially, a compound excellent in transparency is preferred. From thepoint of view of suppressing the change of the retardation caused by thegeneration of stress, a compound with a small photoelastic coefficientis preferred. Incidentally, examples of the preferred compound include:polycarbonate; polyallylate; polysulfone; polyolefin such aspolypropylene; polyester such as polyethylene terephthalate orpolyethylene naphthalate; vinyl alcohol polymer; norbornene polymer;acrylic polymer; styrene polymer; cellulose polymer; mixture polymer oftwo kinds or three or more kinds of the aforementioned polymers; and soon.

[0023] The bonding/lamination of the polarizing element onto thetransparent protective film or onto the retardation film as one ofconstituent members of the transparent protective film is provided forthe purposes of: improving the protecting effect; preventing the opticalaxis from being displaced; preventing foreign matter such as dust or thelike from entering the polarizing element; and so on. For example, thebonding/lamination can be performed by a suitable system such as abonding system using a transparent adhesive layer or the like. Theadhesive agent used in the system is not particularly limited. From thepoint of view of preventing the respective optical characteristics ofthe polarizing element and the transparent protective film fromchanging, a material not requiring any high-temperature process at thetime of curing/drying is preferred and a material not requiring anylong-term curing process or any drying time is preferred. From thispoint of view, a polyvinyl alcohol adhesive agent or tackifier can beused preferably. Incidentally, the adhesive layer for bonding theretardation film and the polarizing element to each other is not shownin FIG. 1.

[0024] As the tackifier, it is possible to use a suitable one that isformed from a suitable polymer such as acrylic polymer, siliconepolymer, polyester, polyurethane, polyether, synthetic rubber, or thelike. Especially, an acrylic trackifier is preferred from the point ofview of optical transparency, tackiness, weather resistance, and so on.Incidentally, as shown in FIG. 1, the adhesive layer 4, especially thetacky layer, may be provided on one or each of opposite surfaces of thepolarizer for the purpose of bonding the polarizer onto a liquid-crystalcell or the like as a subject to be bonded, as occasion demands. In thiscase, a separator or the like may be preferably temporarily attached tothe tacky layer in order to prevent the surface of the tacky layer frombeing contaminated until the surface of the tacky layer is exposed tothe outside and put into practical use.

[0025] Incidentally, as shown in FIG. 1, such transparent protectivefilms provided for suitable purposes such as for improvement inreinforcement, heat resistance, weather resistance, or the like, may bedisposed on opposite surfaces of the polarizing element 1 as occasiondemands. In this case, one of the transparent protective films may beformed, in accordance with the background art, as a coating layer of asuitable resin such as TAC or a layer of a laminate of resin films whenthe transparent protective film is not made of the aforementionedretardation film.

[0026] The transparent protective layer provided in the aforementionedcase preferably has a retardation as small as possible in order tomaintain the above-mentioned compensating effect. If there is someretardation, it is preferable that Nz is 0 or 1 or near 0 or 1. Thetransparent protective layer with Nz of 0 or near 0 is preferablyprovided so that a fast axis of the layer is parallel with theabsorption axis of the polarizing element. The transparent protectivelayer with Nz of 1 or near 1 is preferably provided so that the slowaxis of the layer is parallel with the absorption axis of the polarizingelement.

[0027]FIGS. 2A to 2C are model views each using a Poincare sphere forshowing a state of displacement of the axis of the polarizer owing tothe change of the viewing angle. FIG. 2A shows the polarizer accordingto the present invention. FIGS. 2B and 2C show the background-artpolarizers. That is, FIG. 2B shows the polarizer according to UnexaminedJapanese Patent Publication No. Hei. 4-305602, in which a transparentprotective film having a retardation of from 190 to 320 nm and Nz offrom 0.1 to 0.9 and exhibiting birefringence is disposed so that theslow axis of the transparent protective film is parallel with theabsorption axis of a polarizing element. FIG. 2C shows the polarizer inwhich a film having an in-plane retardation not larger than about 30 nmand having Nz in a range of from 1 to 30 is used as the transparentprotective film.

[0028] In the Poincare sphere, the radius expresses a viewing angle. Thesolid line shows a state in which the apparent angle of the optical axischanges in accordance with the change of the viewing angle viewed fromthe direction of zero degree in the condition that the absorption axis Aof the polarizing element is arranged at 45 degrees. Incidentally, thechange of the optical axis is larger than the actual change forexplanation's sake. Although FIGS. 2A to 2C show the absorption axis Aof the polarizing element and the slow axis S of the retardation film(transparent protective film), the relationship between the transmissionaxis of the polarizing element and the fast axis of the retardation filmalso changes in the same manner as in FIGS. 2A to 2C because thetransmission axis and the absorption axis of the polarizing elementalways form a perpendicularly crossing state and the fast axis and theslow axis of the retardation film always form a perpendicularly crossingstate.

[0029] In each of FIGS. 2A to 2C, the absorption axis A of thepolarizing element changes to become gradually parallel with the viewingangle in accordance with the change of the viewing angle. That is, theangle of the absorption axis A in each of FIGS. 2A to 2C changes largelyfrom its original angle. On the other hand, in the background art shownin FIG. 2C, the angle of the slow axis S3 of the transparent protectivefilm can be regarded as zero degree because the slow axis S3 isgenerated always approximately horizontally with respect to the viewingangle in accordance with the change of the viewing angle. Moreover, theretardation gradually increases in accordance with the change of theviewing angle. When, for example, the maximum value of the retardationis about 40 nm, light α transmitted through the polarizing element issubjected to rotational transformation with the slow axis S3 as itscenter on the Poincare sphere. At this time, the magnitude of the actionvaries in accordance with the wavelength of the light, so that therotational speed of the light increases as the wavelength of the lightdecreases (wavelength dispersion). As a result, the light broadens fromαblue to αred as shown in FIG. 2C. Hence, the perpendicularly crossingrelation in polarized light collapses so that the transmittanceincreases (light leakage)

[0030] On the other hand, in the background art shown in FIG. 2B, theangle of the slow axis S2 of the transparent protective film changes toalways take a value between its original angle and the angle of theabsorption axis A in accordance with the change of the absorption axis Aas shown in FIG. 2B when Nz takes a value (0.75 in FIG. 2B) which is ina range of from 0.1 to 0.9 and which is not smaller than 0.5. In FIG.2B, the change of the slow axis S2 in accordance with the change of theviewing angle is always a half of the change of the absorption axis A.In this case, the influence of the retardation does not appear in thefrontal direction because the optical axis of the transparent protectivefilm coincides with that of the polarizing element, but the influence ofthe retardation appears when the optical axis of the transparentprotective film and the optical axis of the polarizing element aredisplaced from each other.

[0031] In the background art shown in FIG. 2B, the in-plane retardationis equal to about a half wave length of visible light. Hence, light αtransmitted through the polarizing element is subjected to rotationaltransformation by π with the slow axis S2 as its center on the Poincaresphere, so that the angle of the light is compensated so as to be equalto the original angle of the absorption axis A. At the same time, lightwith a shorter wavelength, however, rotates more rapidly because ofwavelength dispersion in the same manner as in FIG. 2C. Hence, the lightbroadens from αblue to αred as shown in FIG. 2B. Hence, when, forexample, the center wavelength is 550 nm, light leakage of blue or redlight occurs.

[0032] On the contrary, the slow axis S21 of the retardation film 21 asone of constituent members of the transparent protective film 2 in thepolarizer according to the present invention changes by an angle largerthan a half of the difference between its original angle and the changedangle of the absorption axis A because Nz of the retardation film is ina range of from 0.8 to 0.95 (0.87 in FIG. 2A). Hence, the change of theaxis owing to the viewing angle always becomes about ¾ as large as thechange of the absorption axis A.

[0033] In the aforementioned case, the influence of the retardationappears along with the axial displacement between the retardation film21 and the polarizing element in the same manner as in FIG. 2B. Hence,light α transmitted through the polarizing element is subjected torotational transformation by π with the slow axis S21 as its center onthe Poincare sphere. As a result, the light broadens from αblue to αredbecause of wavelength dispersion. At the same time, the angle of thelight is compensated so as to be intermediate between the changed angleof the absorption axis A owing to the viewing angle and the originalangle, so that the light is made incident on the next retardation film22 as the other of constituent members of the transparent protectivefilm.

[0034] Because Nz of the retardation film 22 is in a range of from 0.55to 0.7 (0.63 in FIG. 2A), the slow axis S22 of the retardation film 22changes by an angle smaller than a half of the difference between thechanged angle of the absorption axis A and the original angle. Hence,the change of the slow axis S22 owing to the viewing angle is alwaysabout ¼ as large as the change of the absorption axis A. Also in theretardation film 22, the influence of the retardation appears along withthe axial displacement between the retardation film 22 and thepolarizing element, so that the angle of the slow axis S22 becomesintermediate between the angle range of the light αblue to αredsubjected to rotational transformation in the retardation film 21 andthe original angle of the absorption axis A.

[0035] As a result, the light αblue to αred subjected to rotationaltransformation in the retardation film 22 is further subjected torotational transformation by π with the slow axis S22 as its center onthe Poincare sphere. Hence, the light broadens from αblue to αredbecause of wavelength dispersion. The change in this case, however, hasa function for canceling the previous change. Hence, the light iscompensated so as to converge at the original angle of the absorptionaxis A regardless of the wavelength as shown in FIG. 2A. Hence, forexample, even in S the case where the center wavelength is 550 nm, lightleakage of blue or red light is prevented.

[0036] The polarizer according to the present invention can be usedpreferably for the suitable purpose in accordance with the backgroundart, that is, for the purpose of forming a liquid-crystal display deviceor the like. To put the polarizer into practical use, suitablefunctional layers such as a protective layer for various kinds ofpurposes, an anti-reflection layer or/and an anti-glare layer for thepurpose of preventing surface reflection or the like, a light-diffusinglayer, and so on, may be provided on one or both of opposite surfaces ofthe polarizer. The anti-reflection layer can be formed suitably as alight-coherent film such as a fluorine polymer coat layer, a multilayermetal-deposited film, or the like. The anti-glare layer can be alsoformed by a suitable system in which a resin coating layer containingfine particles is applied or a fine roughness structure is provided on asurface by a suitable system such as embossing, sandblasting, etching,or the like, to thereby diffuse surface-reflected light.

[0037] Further, the light-diffusing layer can be also formed in the samemanner as the anti-glare layer. Incidentally, examples of the fineparticles may include inorganic fine particles and organic fineparticles with an average particle size of from 0.5 to 20 μm. Theinorganic fine particles are made of silica, calcium oxide, alumina,titania, zirconia, tin oxide, indium oxide, cadmium oxide, antimonyoxide, etc. and may be electrically conductive. The organic fineparticles are made of crosslinked or non-crosslinked polymers such aspolymethyl methacrylate and polyurethane. One member or a combination oftwo or more members suitably selected from the inorganic fine particlesand the organic fine particles may be used as the fine particles.Incidentally, the anti-glare layer or the light-diffusing layer may beformed to be integrated with the transparent protective film bydiffusion, surface-roughening, or the like, of the transparentprotective film.

[0038] On the other hand, the liquid-crystal display device can beformed by use of the polarizer according to the present inventioninstead of the background-art polarizer and by disposing the polarizeron one or each of opposite sides of the liquid-crystal cell. In thiscase, it is preferable, from the point of view of improvement in displayquality or the like, that the transparent protective film constituted bytwo layers of retardation films is disposed so as to be located betweenthe polarizing element and the liquid-crystal cell. However, thelocation of the transparent protective film is not limited thereto.

REFERENCE EXAMPLE

[0039] A polyvinyl alcohol film was immersed in hot water so as to beswollen. Then, the film was dyed in an aqueous solution ofiodine/potassium iodide and uniaxially drawn in an aqueous solution ofboric acid to thereby obtain a polarizing element. Simplextransmittance, parallel transmittance and cross transmittance of thepolarizing element were measured by a spectrophotometer. As a result,the transmittance was 43.5% and the degree of polarization was 99.9%.

Example 1

[0040] Heat-shrinkable films were bonded to opposite surfaces of apolycarbonate (PC) film through tacky layers respectively. The resultingfilm was uniaxially drawn at 155° C. to thereby obtain a retardationfilm A with an in-plane retardation of 272 nm and Nz of 0.88 withrespect to light with a wavelength of 550 nm (this rule will applyhereunder). On the other hand, the same film as defined above was drawnat 158° C. in the same manner as described above to thereby obtain aretardation film B with an in-plane retardation of 265 nm and Nz of0.62. Then, a TAC film was bonded to one surface of the polarizingelement obtained in Reference Example through a polyvinyl alcoholadhesive agent to thereby form a transparent protective film. Then, theretardation film A was bonded onto the other surface of the polarizingelement through a polyvinyl alcohol adhesive agent and the retardationfilm B was superposedly bonded onto the retardation film A through anacrylic tacky layer to thereby form a transparent protective film. Thus,a polarizer was obtained. Incidentally, the drawing axis in each of theretardation films served as the slow axis, so that bonding was performedso that the slow axis was parallel with the absorption axis of thepolarizing element.

Example 2

[0041] A polarizer was obtained in the same manner as in Example 1except that a retardation film A with an in-plane retardation of 270 nmand Nz of 0.92 obtained by uniaxial drawing at 153° C. and a retardationfilm B with an in-plane retardation of 267 nm and Nz of 0.64 obtained byuniaxial drawing at 156° C. were used in Example 2.

Example 3

[0042] A polarizer was obtained in the same manner as in Example 1except that a retardation film A with an in-plane retardation of 249 nmand Nz of 0.81 obtained by uniaxial drawing at 155° C. and a retardationfilm B with an in-plane retardation of 257 nm and Nz of 0.69 obtained byuniaxial drawing at 158° C. were used in Example 3.

Example 4

[0043] A polarizer was obtained in the same manner as in Example 1except that a retardation film A with an in-plane retardation of 260 nmand Nz of 0.82 obtained by uniaxial drawing at 156° C. and a retardationfilm B with an in-plane retardation of 271 nm and Nz of 0.58 obtained byuniaxial drawing at 160° C. were used in Example 4.

Comparative Example 1

[0044] A polarizer was obtained in the same manner as in Example 1except that the transparent protective film constituted by theretardation films A and B was replaced by a transparent protective filmconstituted by a TAC film with an in-plane retardation of 6 nm and Nz of8.

Comparative Example 2

[0045] A polarizer was obtained in the same manner as in Example 1except that the retardation film A was replaced by a retardation filmwith an in-plane retardation of 265 nm and Nz of 1.01. The retardationfilm was prepared by uniaxially orienting a PC film at 159° C. withoutany heat-shrinkable film bonded thereto.

Comparative Example 3

[0046] A polarizer was obtained in the same manner as in Example 1except that a retardation film A with an in-plane retardation of 630 nmand Nz of 0.91 obtained by uniaxial drawing at 152° C. and a retardationfilm B with an in-plane retardation of 515 nm and Nz of 0.67 obtained byuniaxial drawing at 156° C. were used in Comparative Example 3.

Comparative Example 4

[0047] A polarizer was obtained in the same manner as in Example 1except that the transparent protective film constituted by theretardation films A and B was replaced by a transparent protective filmconstituted by a retardation film with an in-plane retardation of 260 nmand Nz of 0.75. Incidentally, the retardation film was prepared byuniaxial drawing at 158° C. in the same manner as in Example 1.

Evaluation Test

[0048] The spectroscopic intensity in the polarizer obtained in each ofExamples 1 to 4 and Comparative Examples 1 to 4was measured by anapparatus shown in FIG. 3. That is, parallel rays were generated by acombination of a light source K, a pinhole P and lenses R. The parallelrays were made incident, through a Glan-Thompson prism G, onto a sampleS constituted by the polarizer obtained in each of Examples 1 to 4 andComparative Examples 1 to 4. Light transmitted through the sample S wasreceived by a detector D through a spectroscope B, so that thespectroscopic intensity of the light was measured. Incidentally, for themeasurement, the sample S was mounted onto a rotary stage capable ofrotating by β around a rotation axis γ perpendicular to the parallelrays so that the transparent protective film constituted by theretardation film(s) was disposed on the light source side so as to beperpendicular to the light rays and so that the absorption axis of thepolarizing element formed 45 degrees with respect to the rotation axisγ. The Glan-Thompson prism G was disposed so that its transmission axiswas parallel with the absorption axis of the sample S to thereby formthe relation of crossed-Nicol.

[0049] Transmittance was calculated from the ratio of the spectroscopicintensity measured as described above to reference spectroscopicintensity. L, a and b were calculated from the transmittance value onthe basis of three stimulus values, so that the color difference ΔE0from a black point was obtained. On the other hand, spectraltransmittance was measured in the same manner as described above in thecondition that the sample S was rotated by 75 degrees around therotation axis γ. Hence, the color difference ΔE75 from a black point wasobtained. At the same time, the color difference ΔE75-0 was calculatedfrom the color coordinates at the respective rotation angles of 0 degreeand 75degrees on the basis of results of the aforementioned measurement.Incidentally, the reference spectroscopic intensity was based on thespectroscopic intensity of the apparatus in the condition that theGlan-Thompson prism G and the sample S were removed from the apparatusshown in FIG. 3, that is, in the condition that the apparatus had thelight source K, the pinhole P, the lenses R, the spectroscope B, and thedetector D.

[0050] Results of the above description were shown in the followingtable. Color Rotation Angle of 0 degree Rotation Angle of 75 degreesDifference L A b ΔEO L a b ΔE75 ΔE75-0 Example 1 1.969 1.428 −1.2062.715 2.011 1.431 −1.332 2.805 0.133 Example 2 1.782 1.572 −1.185 2.6552.013 1.218 −1.203 3.293 1.090 Example 3 1.824 1.478 −1.239 2.655 2.6191.631 −1.375 3.378 0.821 Example 4 2.010 1.428 −1.032 2.673 2.910 1.294−1.432 3.492 0.904 Comparative 1.982 1.327 −1.032 2.599 9.214 2.6753.923 10.365 8.870 Example 1 Comparative 1.895 1.414 −1.197 2.650 7.1102.945 3.139 8.311 6.953 Example 2 Comparative 2.588 1.845 −1.715 3.61217.25 9.311 4.316 20.072 17.524 Example 3 Comparative 1.688 1.521 −1.1502.547 2.825 4.911 −6.316 8.485 6.283 Example 4 Comparative Example 5

[0051] It is apparent from the Table and results of the eye observationthat difference was hardly recognized between the color difference ΔE0from a black point in the frontal direction in each of Examples 1 to 4and the color difference ΔE0 in each of Comparative Examples 1 to 4 butthe color difference ΔE75 in the direction of 75 degrees in each ofExamples 1 to 4 was obviously smaller than that in Comparative Example 1showing a general polarizer or in Comparative Example 2 showing anotherkind of polarizer, that is, light leakage was suppressed in Examples 1to 4. Hence, when Nz is not smaller than 1 as shown in each ofComparative Examples 1 and 2, the compensating effect cannot be found.On the other hand, the color difference ΔE75 in Comparative Example 3was larger than that in each of Comparative Examples 1 and 2. It isapparent that the compensating effect cannot be found also when theretardation exceeds a predetermined value.

[0052] On the other hand, in Comparative Example 4, the color differenceΔE75 was smaller than that in Comparative Example 1 but the values of aand b were large so that transmitted light was discolored to violet evenin eye observation. This means that there is no optimal compensation forthe blue or red region. It was confirmed that the color difference ΔEgradually increased and discoloring (light leakage) gradually increasedin eye observation as the rotation angle increased within a rangebetween 0 degree and 75 degrees. On the contrary, in Examples 1 to 4,the color of transmitted light was substantially near to an achromaticcolor and the values of a and b were smaller than those in ComparativeExample 4. It is apparent that the compensating effect was achieved in awide-range visible light region in Examples 1 to 4. It is apparent fromthe above description that a polarizer capable of preventing lightleakage owing to the change of the viewing angle in a wide-range visiblelight region can be obtained according to the present invention.

[0053] Although the invention has been described in its preferred formwith a certain degree of particularity, it is understood that thepresent disclosure of the preferred form can be changed in the detailsof construction and in the combination and arrangement of parts withoutdeparting from the spirit and the scope of the invention as hereinafterclaimed.

What is claimed is:
 1. A polarizer comprising: a polarizing element; andat least one transparent protective film constituted by two layers ofretardation films with an in-plane retardation in a range of from 190 to320 nm with respect to light having a wavelength of 550 nm, saidtransparent protective film being bonded onto one of opposite surfacesof said polarizing element so that a slow axis of each of saidretardation films is parallel with an absorption axis of said polarizingelement, said two layers of retardation films being constituted by acombination of a retardation film with Nz of from 0.8 to 0.95 and aretardation film with Nz of from 0.55 to 0.7 in a condition of nx>ny andNz=(nx−nz)/(nx−ny) in which nx and ny are in-plane refractive indices ofsaid retardation films respectively, and nz is a refractive index in adirection of thickness of each of said retardation films.
 2. A polarizeraccording to claim 1, wherein said retardation film with Nz of from 0.8to 0.95 is disposed on a polarizing element side.
 3. A polarizeraccording to claim 1, wherein said polarizing element isabsorption-dichromatic.
 4. A polarizer according to claim 3, whereinsaid absorption-dichromatic polarizing element is made of a uniaxiallydrawn film of a polyvinyl alcohol compound containing iodine ordichromatic dye.